Utilization of Libyan Grass Fibers in Styrene–Butadiene Rubber Composites: Correlation Between Filler Content and Mechanical Properties

Abstract

In this study, local Libyan non-woody grasses—Retama raetam (known as R’tem), Stipa tenacissima (known as Halfa) or Stipagrostis pungens (known as Esbat)—were used as a reinforcement filler in styrene-butadiene rubber (SBR) composites. Motivated by previous investigations done by our group, this study aims to compare the reinforcing behavior of these three cost-effective and locally available grasses.  A correlation analysis was carried out to establish the relationship between filler type and its loading with mechanical properties of the resultant composites. Composites were prepared using a twin-screw extruder with filler loadings of 10, 20, 30, and 40 wt.% relative to polymer and its mechanical properties, namely: stress at break, elongation at break, impact strength, and micro-hardness were evaluated. The correlation analysis was performed using Pearson’s method to determine the coefficient of determination (R²). Results showed that the correlation between the composite’s performance and the fiber content is strongly dependent on fiber type. In general, composites made with Halfa or Esbat showed a strong relationship with all measured properties except that with the stress at break. Whereas composites made with R′tem exhibited a very strong relationship with all properties except that with the impact strength. Contrary, Halfa- or Esbat-reinforced composites showed a very weak relationship between the fiber content and the stress at break (R² = 0.0238 and 0.0629, respectively). However, R’tem-filled composites showed a linear decrease in stress at break with increasing fiber content, demonstrating a strong correlation (R² = 0.9947). similarly, elongation at break decreased consistently with increasing filler loading for all composites irrespective to the fiber type, where all composites showed R² > 0.80.  Here, R’tem-filled composites displayed the strongest relationship between the elongation at break and the fiber content. Similarly, composites showed a strong linear relationship between the impact strength and fiber loading with R² > 0.80,